Thrust reversers commonly used on commercial aircraft engines are generally of two types. A first, newer type of thrust reverser for jet engines generally comprises a pair of thrust reverser door members which are pivotally mounted to the rear of an engine about an axis which is substantially diametrical with respect to the exhaust nozzle of the engine. These thrust reverser doors having scarfed trailing edges in order to allow the doors to pivot between stowed and deployed positions, and the thrust reverser also includes a pair of pivotally mounted half shells surrounding at least the trailing edges of the thrust reverser doors and defining a planar exhaust outlet for the engine. In this type of thrust reverser, the throat area of the exhaust outlet is defined either by the half shells, or partly by the doors and the half shells.
A second, older type of thrust reverser comprises only a pair of thrust reverser doors which are pivotally mounted on an engine about an axis which is substantially diametrical with respect to the exhaust nozzle of the engine, but without the half shells. The doors also have scarfed trailing edges in order to allow the pivoting between stowed and deployed positions.
This present invention relates to an improved thrust reverser of either type for jet engines, especially the kind used on aircraft. More particularly, the invention relates to a thrust reverser which integrates a connecting mechanism enabling the trimming or adjusting of the area of the throat of the exhaust outlet. This exhaust outlet can be defined by the thrust reverser doors alone, or by the exhaust nozzle only (formed and defined by two half shells surrounding the reverser doors), or by the combination of thrust reverser doors and exhaust nozzle.
In order to reduce the landing distance of a jet powered aircraft as well as to increase the level of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized on the jet engines in order to provide a braking thrust for the aircraft. Typically, such thrust reversers are formed by thrust reverser doors or by a combination of thrust reverser doors and a pair of half shells. The reverser doors are capable of pivoting between two positions about an axis which is transverse to the longitudinal or thrust axis of the engine, and substantially diametrically positioned with respect to the jet of the engine.
In the first position, the doors (or the doors with the two half shells as described in U.S. Pat. No. 5,176,340) are in a stowed position, out of the direct path of the exhaust blast of the engine. In this position, the doors when not fitted with the two half shells, or the doors and the two half shells form the exhaust nozzle of the engine so that the thrust of the engine is directed rearward, thereby producing the forward thrust of the aircraft. In the second or deployed position, the doors are pivoted about the pivot axis to a transverse, blast deflecting or deployed position, to intercept and redirect the jet blast and produce the aerodynamic braking rust of the aircraft when called for by the pilot of the aircraft. The invention deals only with the first position, i.e. the stowed position, and allows for trimming of adjustment of the thrust reverser to a specific engine.
The prior art discloses non-adjustable or non-trimmable exhaust area nozzles for thrust reversers. For example, U.S. Pat. Nos. 4,129,269 and 5,176,340 show the type of thrust reverser which can benefit from the present invention. The thrust reversers shown in these two patents are designed, developed and manufactured for a specific engine and for precise engine specifications. This can be a drawback, however, since during the development of new engines, the engine manufacturer does not accurately know what will be the final required throat area of the exhaust nozzle. Since the exhaust nozzle is formed by either the thrust reverser doors, or the thrust reverser doors and their associated half shells (U.S. Pat. No. 5,376,340), and since the exhaust nozzle is usually designed, developed and manufactured at the same time as the design, development and manufacture of a new engine, the throat area is designed to an estimated value.
But, when the engine and thrust reverser get to the final stage of development and are ready for manufacture, and the time arrives to mate the thrust reverser to the engine, changes often have taken place in the engine design specifications which require corresponding changes to the thrust reverser before it can be properly fitted to the engine. This can be extremely costly and detrimental to the program schedule, to redesign and hence remanufacture the thrust reverser exhaust nozzle to the final throat area, to accommodate even a 2 or 3 percent change in the throat area
The prior art also discloses some variable area exhaust nozzles for thrust reversers as shown for example in U.S. Pat. Nos. 5,181,676 and 4,966,327. A variable area exhaust nozzle provides certain benefits for the jet engines, in enabling them to adapt and optimize their performance to different conditions of the flight, for example during take-off, climb and cruise. The variable area exhaust provides also a trimming capability to the exhaust nozzle, allowing each production thrust reverser exhaust nozzle to be fully optimized with the production engine on which it will be installed. While this capability eliminates some of the above described drawbacks, the prior art also requires the utilization of actuation controlling devices to accomplish the trimming or to vary the throat area of the exhaust nozzle. This in turn is a factor which increases both the cost and the weight of the thrust reverser and the engine assembly.
Due to manufacturing tolerances the basic engine parameter of thrust versus low rotor compressor (fan) speed (N-1) varies from engine to engine. A trimmable nozzle will allow the engine manufacturer to adjust the mass air flow and the engine pressure ratio so that each engine delivered will produce rated thrust at rated N-1. Also with the normal engine usage, engine performance erodes with time. A trimmable nozzle will allow recovery of some degraded engine performance by simply carrying out the adjusting method of this invention on the nozzle.
Accordingly, a primary object of the present invention is to provide a thrust reverser that overcomes the aforementioned disadvantages of prior art thrust reversers.
A further object of the invention is to provide a thrust reverser which integrates a trimming capability for the exhaust nozzle.
Still another object of the invention is to provide a thrust reverser having trimming capability for the exhaust nozzle without the utilization of actuators or actuation controlling devices.
Still another object of the invention is to provide a thrust reverser construction wherein the structure which is holding the reverser exhaust nozzle has the capability of allowing the trimming of the throat area of the exhaust nozzle, without re-design of the reverser, to ensure therefore at low cost, that the exhaust area has the same value as the one finally chosen by the engine manufacturer.
Yet another object of the invention is to ensure, through the trimming capability of the exhaust nozzle, that each production thrust reverser exhaust nozzle is fully optimized with the production engine on which it will be installed.
Yet another object of the invention is to ensure, through the trimming capability of the exhaust nozzle, that the normal and known engine performance degradation over time can be easily compensated.
Still a further object of this invention is to provide an improved method for trimming the throat area value of the engine nozzle for an engine equipped with a thrust reverser.
These and other objects and advantages of this invention will become apparent from a consideration of the following description of the invention.